Peak detector for resolution enhancement of ultrasonic visualization systems

ABSTRACT

A digital electronic system for improving the resolution and dynamic range-handling capacity for received ultrasound in reflection or transmission imaging system. This system provides a means for preventing loss of structural detail in the display by minimizing the overlapping of signals resulting from the transducer bandwidth and pulse length. It also makes use of a (positive or negative) peak detector to recognize and print as a single point the presence of point targets. With the present technology, a point target may be represented in a B-mode display on several successive scan lines resulting in an abnormally large representation on the display. The actual target is represented by the peak point of the envelope of a series of scan lines in which the point target is displayed. The objective is to print only one point which corresponds with the actual position of the point target and with an intensity that corresponds to the intensity of the received signal. In general, dynamic range compression is required to prevent the wide intensity range of the received ultrasound from either saturating or overdriving the display. To accomplish this objective the received signal amplitudes are continually digitized and stored so that three successive lines of data can be compared. At any given instant of time, three resolution elements from each of these three successive lines are compared. A signal to print is transmitted to the display if the center resolution element of the three-by-three array is equal to or in excess of the surrounding eight resolution elements. The amplitude of the displayed point is established by a transfer function programmed into the system.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is in the field of ultrasonic visualization systems.

2. Description of the Prior Art

In a typical reflection ultrasonic display utilizing a series of B-modelines, an acoustic pulse is directed at a target or specimen and thereturning echoes received are displayed along the scan line. Thefundamental frequency of the transmitted pulse is typically in the onemegahertz to ten megahertz range. The resulting echoes (r.f.) aredetected and the detected (video) signal utilized to produce a displaysuch as on a storage oscilloscope where each line is displayed andstored sequentially to produce a complete view.

A typical Z-axis, or brightness, sensitivity range for an oscilloscopedisplay might be from a 1 volt saturation level to a 0.1 volt minimumdetected voltage to produce an indication on the screen. The ultrasonicreflection from a glass target might be as high as 20 volts while thereflection from a biological target might be as low as 20 microvolts.This 120 decibel difference in received voltage cannot be directlydisplayed on the scope whose full range is only 20 decibels. Thealternatives heretofore utilized have been compression of the range ofreceived voltages, rendering differences in intensity impossible todistinguish, and selection of a pair of thresholds above the 0.1 voltminimum received voltage and below the 1 volt maximum received voltage.In this case, where the received voltage exceeds the selected fullbrightness voltage for the oscilloscope, a large area of the screen willbe illuminated, while for other reflections below the selected thresholdno indication will be displayed of received ultrasound.

SUMMARY OF THE INVENTION

One embodiment of the present invention is a peak detector system forultrasonic visualization arrangements comprising first means for storingan electrical representation of received ultrasonic energy which isdetected after it has been directed over an area of a target, secondmeans for comparing values of said representations and otherrepresentation indicative of received ultrasonic energy which isdetected after it has been directed at the target, and third means forproducing an output signal, operable to be utilized by a display,indicative of inflection points determined by said second means forcomparing.

The larger reflection ultrasound values mentioned above are generallythe result of specular reflection, while the generally more desirablescatter reflections indicative of surface texture for a target areconsiderably lower in amplitude. In order to prevent such desirablescatter reflection signals from falling below the threshold voltage forthe display system or exceeding the saturation level of the display,perhaps because of arriving at the transducer superimposed upon a largespecular reflection, the present system endeavors to only detect the(positive or negative) peaks of the reflected wave form. This enablesthe production of a useable display signal that provides visualinformation on the surface details of structures being viewed.

In order to determine these maxima (or minima), each line of receivedechoes is divided into digital resolution elements and a series ofcomparisons performed to locate the maxima, without regard to absolutevalues of an area of many resolution elements relative to other largeareas. In this manner only resolution elements having a value greaterthan or equal to the immediately surrounding resolution elements will beselected as a peak point. The absolute value of this peak point is thencoupled either directly to a display or, preferably, to a memory devicewhich contains one or more transfer functions for converting certainabsolute values of reflection to predetermined alternate values whichpermits the expansion of certain ranges of reflections and thecompression of others so that various ranges of reflection values may beemphasized.

It is an object of the present invention to provide an ultrasonicvisualization system which effectively enhances the resolutioncapabilities of the display by detecting and displaying the inflectionpoints of received ultrasound.

It is a further object of the present invention to provide such a systemwherein the brightness of the display for such inflections may be varieddepending upon a selected transfer function in order to compress thewide dynamic range typical of ultrasonic signals into the relativelynarrow dynamic range of the diplay devices. The system may offer aninfinite number of transfer functions from which the optimum transferfunction may be selected to best display the data of diagnosticsignificance.

Further objects of the present invention shall be apparent from thefollowing detailed description and accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an embodiment of the present resolutionenhancement system.

FIG. 2 is a diagrammatic illustration of the resolution improvementobtainable utilizing a system as embodied in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiment illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, such alterations and furthermodifications in the illustrated device, and such further applicationsof the principles of the invention as illustrated therein beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates.

Referring in particular to FIG. 1, there is shown an ultrasound unit 11including an ultrasonic transducer coupled from a pulser which emitsultrasonic pulses at a target at a synchronized rate. The transducer, ora separate transducer, receives reflection or transmission imagingultrasonic pulses returning after incidence with the target and convertsthese received pulses to an electrical signal which is detected withinthe ultrasound unit 11. The detected wave form, which is essentially anenvelope of the one megahertz to ten megahertz fundamental frequencyultrasound pulses, is coupled to an analog-to-digital converter 12.Analog-to-digital converter 12 operates at a high digitizing rate, inthe exemplary embodiment at ten megahertz. This generates one"resolution element" for each 1/10 of a microsecond. Each line of datato be displayed is therefore divided into a series of resolutionelements at each 1/10 of a microsecond. Such an analog-to-digitalconverter which may be utilized is manufactured by Biomation of PaloAlto, California and is utilized, for example, in their model 610transient recorder.

A clock and address generator 13 serves to synchronize not onlyoccurrence of the resolution elements for each line but also the timingof the lines themselves. A sync signal is provided on line 14 tocoordinate the firing of a transmitted ultrasonic pulse to initiate eachline. The spacing between transmitted pulses depends upon the depth towhich the specimen or target is to be viewed, due to the inherent delaytime in the return of the reflected sound from the target. Throughoutthe description of the preferred embodiment hereinafter, reference willbe made to received ultrasonic echoes from a target but it should beunderstood that transmission imaging is as useful with the presentresolution enhancement system as is echo or reflection imaging.

Clock and address generator 13 also receives a pulse repetition ratecontrol signal from the ultrasound unit on line 16 which indicates thepulse repetition rate of the ultrasound unit so that the generator 13may produce the appropriate sync signal. Clock and address generator 13further synchronizes the analog-to-digital converter resolution elementrate with the resolution element storage in RAMS 17 and 18 and alsosyncs the other circuits such as the compare circuit 42, PROM 44 and theD/A converter and display.

Referring briefly to FIG. 2, this diagram shows a series of scan linesobtained by moving a transducer across a point target. The lateralrepresentation of a Rayleigh scatterer is in effect a beam plot of thetransducer, whereas the desired response is a single point correspondingin range and intensity to the peak point of the lateral analog envelope.The transmitted pulses, as shown at 19, impinge upon the target 21 astransducer 22 is moved downwardly in the direction shown. The echoesfrom the target are shown generally at 23, and it can be seen that themaximum echo occurs when the transducer beam is aimed most directly atthe target. The envelope wave form shown at 24 is generally thatobtained from the detector of the ultrasound unit. The threshold andsaturation levels for the oscilloscope display may be selected at anypair of heights between the base line 26 and the peak 27 if some portionof this point target response is to be shown on the oscilloscope screen.

For example, the lower threshold may be selected at a level such as 28and saturation at a level such as 29. In this fashion, the oscilloscopescreen would begin to be lit at the level of line 28 with increasingbrightness up through the level at 29, and the peak of the envelopeabove line 29 (or the the left as shown in FIG. 2) would be of uniformmaximum brightness.

The desired display for this point target, however, would be a point atthe peak of the envelope as indicated at 27. The system illustrated inFIG. 1 will segmentize a given line into the above mentioned resolutionelements to compare adjacent resolution elements to determine a peak.This is not illustrated in FIG. 2 since a single point target is shown,and one echo from the target per line occurs in this idealizedsituation. However, the system of FIG. 1 further compares adjacent linesas to corresponding resolution elements which occur "side-by-side" suchas those along area 23 of the figure. Therefore, the system of FIG. 1would determine that a maximum inflection point occurs at 27 and providea signal to the oscilloscope display calling for illumination of thatpoint on the screen. The brightness of the point may be determined insome linear fashion or, preferably, one or more transfer functions maybe programmed into a memory such as a PROM to provide a nonlineartransfer function which emphasizes particular portions of the response.

Returning now to FIG. 1, at a frequency of line repetition of onekilohertz, or one millisecond per line, as a maximum, 10,000 six bitwords must be stored in each of RAM 17 and 18. At higher linefrequencies, there would be fewer resolution elements per line and henceless storage necessary. In any event, analog-to-digital converter 12outputs a six bit word indicative of the analog value of received anddetected voltage from the transducer ultrasound unit 11 onto lines 31and 32 each tenth of a microsecond. RAM 17 stores these six bitresolution elements in appropriately addressed locations as determinedby the address generator 13. Resolution elements already stored in RAM17 are transferred to corresponding addressed resolution elementlocations in RAM 18 as the new element values reach RAM 17 on line 31.

As can be seen, when the resolution elements of the first line arrive,they are provided to the shift registers on line 32, as shall bediscussed hereinafter, and also to RAM 17. When the second line of dataarrives, this data is also coupled on line 32 to the shift registers andon line 31 to RAM 17. As the various locations are addressed bygenerator 13, RAM 17 transfers the values from the first line to RAM 18while the values for the second line are placed in RAM 17. When thethird line of data arrives, it also is moved on line 32 to the shiftregisters and on line 31 into RAM 17. The second line data is thereupontransferred from RAM 17 to RAM 18 (and also to shift registers) whilethe first line of data is moved from RAM 18 to its set of shiftregisters.

As each six bit word is coupled from analog-to-digital converter 12 online 31 to RAM 17, it is also provided on line 32 to shift register 33.The preceding value in register 33 is shifted to register 34 etc.Similarly, the information for corresponding resolution elements on theprevious line are coupled from RAM 17 to shift registers 36 to 38, andthe resolution element values for the line previous to that are coupledfrom RAM 18 to shift registers 39 through 41.

Thus, for example, at a given moment, shift registers 33 through 35might have resolution elements 81, 82 and 83 in registers 35, 34 and 33respectively, for line 11 of the display. At that time, the values forresolution elements 81, 82 and 83 would be in shift registers 38, 37 and36, respectively, for line 10, and the values for resolution elements81, 82 and 83 would be in shift registers 41, 40 and 39, respectively,for display line 9. These nine digital values are compared by acomparison circuit 42, and if the value from register 37 is greater thanor equal to the other eight register values, then the digital value iscoupled on line 43 to PROM 44. It can be seen that the value in register37 is the value for the resolution element which is in the center of athree-by-three array of resolution elements. If a minimum or negativepeak point were to be sought, of course, the criterion would be for thecenter point to be less than or equal to each of the eight others.

The analog-to-digital converter 12 produces the ten megahertz resolutionelement values resulting in a continuous scan and comparison of theseblocks of three-by-three arrays over the entire display as they arereceived. The registers may be, for example, type 74174 integratedcircuits and are synchronized by address generator and clock 13. Anexample of a 74174 is an N74174 hex D-type flip-flop with clearmanufactured by Signetics Corporation, Sunnyvale, California.

The compare circuit 42 is a set of eight comparators comparing the valuein register 37 to each of the other eight register values. Type 7485comparators may be utilized in pairs since six bit words must becompared. An example of a 7485 is an N7485 4-bit magnitude comparatormanufactured by Signetics Corporation. The comparators are alsosynchronized through the operation of the clock and address generator13. PROM 44, in the exemplary embodiment, is divided into eight sectionswith the most significant portion of the PROM addresses being input onthe compression select line 46 so that one of eight transfer functionsmay be selected. Then, if a legitimate maximum point is obtained fromthe compare circuitry 42, the six-bit value for that point is coupledfrom the output of compare circuitry 42 on line 43 to the PROM. That sixbit word is utilized to address a particular storage location in theselected section of the eight transfer function sections. Thus, adesired scale of brightness is provided by the values stored in thePROM, and the actual value of the maximum point is converted to itsappropriate value on that scale in PROM 44.

The selected output is then coupled on line 47 to a digital-to-analogconverter which provides an analog voltage to effect the proper amountof beam current and illumination on the oscilloscope screen in display49. Other uses, of course, may be made of the output value for othertypes of displays, etc.

In regard to RAMS 17 and 18 in the system, the very high data raterequired by the peak detection system places a stringent requirement onthe memory subsystem. While there are bi-polar memory types whichapproach or even exceed the required speeds, the required size of thememory (about 120,000 bits) makes the cost of these bi-polar typesprohibitive. Therefore, less expensive MOS memory may be utilized forthis application and a standard "memory interleaving" technique used toaccommodate the lower speed of this memory type.

The technique comprises writing successive data words (six bit binaryrepresentations of the signal sample amplitude) into different memoryblocks in a cyclic pattern so that if N memory blocks are used, eachblock handles data at 1/N times the system data rate. Since each of theN blocks is required to store 1/N times as many data words, the totalsystem capacity requirement remains the same (that is, approximately120,000 bits of memory).

Type 74174 bi-polar latches, which may be thought of as small, highspeed buffer memory elements of one data word capacity each, are used atthe input and output of each memory block to hold information for thetime required to read a data word out of the slow MOS memory and replaceit with a new data word.

The CCD460A memory devices utilized require a read-modify-write cyclewhich is about three to four times that allowed by the data rate of 10million data words per second. Therefore, four interleaved blocks ofmemory are used for each "line" of data. Because each data word consistsof six bits and each memory device is organized to accept a four bitdata word, one and one half memory devices are required for each blockof memory. For the two lines of data the required number of memorydevices is therefore one and a half memory devices per block times fourblocks per line times two lines, or twelve memory devices.

Since the memory is being used as a digital delay line, the number ofdata words each device can store must be adequate for the longest delayrequired by the system. For a one millisecond delay in each line and adata rate of 10 million words per second, 10,000 data words per line arerequired. Each memory device can store 4,096 four-bit words. Therefore,four blocks per line provide 16,384 data words per line which isadequate. The system is designed so that the number of data words ofstorage which are used may be varied, thereby varying the delay time.

While there have been described above the principles of this inventionin connection with specific apparatus, it is to be clearly understoodthat this description is made only by way of example and not as alimitation in the scope of the invention.

What is claimed is:
 1. A peak detector system for ultrasonicvisualization arrangements comprising:a. first means for dividingreceived ultrasonic energy into resolution elements; b. second means forcreating for each resolution element a plural bit word which encodes thevalue of the received ultrasonic energy in the resolution element; c.third means for storing said plural bit words; and d. fourth meansconnected to said third means for comparing said plural bit words andproducing at its output a signal indicative of peak points determined bysaid fourth means for comparing.
 2. The system of claim 1 which furthercomprises fifth means coupled to the output of said fourth means forconverting the output of said fourth means to a different valueaccording to a predetermined transfer function.
 3. The system of claim 1in which said received ultrasonic energy is in lines and in which saidthird means stores resolution elements from two successive lines andsaid fourth means includes means for comparing corresponding resolutionelements of the two successive lines.
 4. The system of claim 3 in whichsaid fourth means also includes means for comparing a resolution elementin one line with a resolution element adjacent the correspondingresolution element of a successive line.
 5. The system of claim 4 inwhich said fourth means compares a resolution element with its adjacentresolution elements within a line and the corresponding three resolutionelements of the previous and successive lines.
 6. The system of claim 5which further comprises fifth means coupled to the output of said fourthmeans for converting the output of said fourth means to a differentvalue according to a predetermined transfer function.
 7. The system ofclaim 6 in which said fifth means includes means for selecting atransfer function from a plurality of transfer functions.
 8. The systemof claim 7 in which said fifth means includes a PROM.
 9. A peak detectorsystem for line scanning ultrasonic visualization arrangementscomprising:a. means for storing multiple levels of an electricalrepresentation of ultrasonic energy received from a line scanningdevice, said corresponding multiple levels being related to the valuesof the received ultrasonic energy within each line of energy received;b. means for comparing levels in one stored line with levels in anadjacent line; c. means for producing an output signal indicative ofpeak points determined by said means for comparing.
 10. The system ofclaim 9 in which said means for comparing includes means for comparinglevels in three lines and producing an output equal to the highest levelwhen peak points are determined.
 11. The system of claim 10 in whichsaid means for comparing also includes means for comparing levels withina line for indicating peak points.